286 research outputs found
Outflows from active galactic nuclei: The BLR-NLR metallicity correlation
The metallicity of active galactic nuclei (AGNs), which can be measured by
emission line ratios in their broad and narrow line regions (BLRs and NLRs),
provides invaluable information about the physical connection between the
different components of AGNs. From the archival databases of the International
Ultraviolet Explorer, the Hubble Space Telescope and the Sloan Digital Sky
Survey, we have assembled the largest sample available of AGNs which have
adequate spectra in both the optical and ultraviolet bands to measure the
narrow line ratio [N II]/H{\alpha} and also, in the same objects, the
broad-line N V/C IV ratio. These permit the measurement of the metallicities in
the NLRs and BLRs in the same objects. We find that neither the BLR nor the NLR
metallicity correlate with black hole masses or Eddington ratios, but there is
a strong correlation between NLR and BLR metallicities. This metallicity
correlation implies that outflows from BLRs carry metal-rich gas to NLRs at
characteristic radial distances of ~ 1.0 kiloparsec. This chemical connection
provides evidence for a kinetic feedback of the outflows to their hosts. Metals
transported into the NLR enhance the cooling of the ISM in this region, leading
to local star formation after the AGNs turn to narrow line LINERs. This
post-AGN star formation is predicted to be observable as an excess continuum
emission from the host galaxies in the near infrared and ultraviolet, which
needs to be further explored.Comment: 19 pages, 13 figures, 3 tables. Accepted for publication at MNRA
1-[4-(4-ChloroÂbutÂoxy)-2-hyÂdroxyÂphenÂyl]ethanone
In the title compound, C12H15ClO3, the ethÂoxy group is nearly coplanar with the benzene ring, making a dihedral angle of 9.03 (4)°, and is involved in an intraÂmolecular O—H⋯O hydrogen bond to the neighbouring hyÂdroxy group
Star Formation in Self-Gravitating Disks in Active Galactic Nuclei. II. Episodic Formation of Broad-Line Regions
This is the second in a series of papers discussing the process and effects of star formation in the self-gravitating disk around the supermassive black holes in active galactic nuclei (AGNs). We have previously suggested that warm skins are formed above the star-forming (SF) disk through the diffusion of warm gas driven by supernova explosions. Here we study the evolution of the warm skins when they are exposed to the powerful radiation from the inner part of the accretion disk. The skins initially are heated to the Compton temperature, forming a Compton atmosphere (CAS) whose subsequent evolution is divided into four phases. Phase I is the duration of pure accumulation supplied by the SF disk. During phase II clouds begin to form due to line cooling and sink to the SF disk. Phase III is a period of preventing clouds from sinking to the SF disk through dynamic interaction between clouds and the CAS because of the CAS overdensity driven by continuous injection of warm gas from the SF disk. Finally, phase IV is an inevitable collapse of the entire CAS through line cooling. This CAS evolution drives the episodic appearance of broad-line regions (BLRs). We follow the formation of cold clouds through the thermal instability of the CAS during phases II and III, using linear analysis. Since the clouds are produced inside the CAS, the initial spatial distribution of newly formed clouds and angular momentum naturally follow the CAS dynamics, producing a flattened disk of clouds. The number of clouds in phases II and III can be estimated, as well as the filling factor of clouds in the BLR. Since the cooling function depends on the metallicity, the metallicity gradients that originate in the SF disk give rise to different properties of clouds in different radial regions. We find from the instability analysis that clouds have column density NH ≲ 1022 cm–2 in the metal-rich regions whereas they have NH ≳ 1022 cm–2 in the metal-poor regions. The metal-rich clouds compose the high-ionization line regions whereas the metal-poor clouds are in low-ionization line (LIL) regions. Since metal-rich clouds are optically thin, they will be blown away by radiation pressure, forming the observed outflows. The outflowing clouds could set up a metallicity correlation between the BLRs and narrow-line regions. The LIL regions are episodic due to the mass cycle of clouds with the CAS in response to continuous injection by the SF disk, giving rise to different types of AGNs. Based on Sloan Digital Sky Survey quasar spectra, we identify a spectral sequence in light of emission-line equivalent width from phase I to IV. A key phase in the episodic appearance of the BLRs is bright type II AGNs with no or only weak BLRs, contrary to the popular picture in which the absence of a BLR is due to a low accretion rate. We discuss observational implications and tests of the theoretical predictions of this model
Star formation in self-gravitating disks in active galactic nuclei. II. Episodic formation of broad line regions
(abridged) We study the consequence of star formation (SF) in an self-gravity
dominated accretion disk in quasars. The warm skins of the SF disk are governed
by the radiation from the inner part of the accretion disk to form Compton
atmosphere (CAS). The CAS are undergoing four phases to form broad line
regions. Phase I is the duration of pure accumulation supplied by the SF disk.
During phase II clouds begin to form due to line cooling and sink to the SF
disk. Phase III is a period of preventing clouds from sinking to the SF disk
through dynamic interaction between clouds and the CAS. Finally, phase IV is an
inevitable collapse of the entire CAS through line cooling. This CAS evolution
drives the episodic appearance of BLRs. Geometry and dynamics of BLRs can be
self-consistently derived from the thermal instability of the CAS during phases
II and III by linear analysis. The metallicity gradient of SF disk gives rise
to different properties of clouds from outer to inner part of BLRs. We find
that clouds have column density N_H < 10^22cm^{-2} in the metal-rich regions
whereas they have N_H > 10^22 cm^{-2} in the metal-poor regions. The metal-rich
clouds compose the high ionization line (HIL) regions whereas the metal-poor
clouds are in low ionization line (LIL) regions. Metal-rich clouds in HIL
regions will be blown away by radiation pressure, forming the observed
outflows. The LIL regions are episodic due to the mass cycle of clouds with the
CAS in response to continuous injection by the SF disk, giving rise to
different types of AGNs. Based on SDSS quasar spectra, we identify a spectral
sequence in light of emission line equivalent width from Phase I to IV. A key
phase in the episodic appearance of the BLRs is bright type II AGNs with no or
only weak BLRs. We discuss observational implications and tests of the
theoretical predictions of this model.Comment: 27 pages in emulateapj style, 10 figures, Accepted by ApJ 201
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